How can you tell if a chemical compound is ionic or covalent by just looking at the formula?

Under what conditions will a gas be most likely to exhibit the ideal gas properties predicted by the ideal gas law? 1)high pressures and high temperature, because particles are forced closer together with higher kinetic energy, so intermolecular forces of attraction are weaker 2)high pressure and low temperature, because particles are forced closer together and moving slower, so the volume of the particles is less significant 3) low pressure and high temperature, because particles are spread farther apart and moving faster, so the intermolecular forces of attraction are weaker 4)low pressure and low temperature, because particles are spread farther apart with lower kinetic energy, so the volume of the particles is less significant